1. Field of the Invention
The present invention relates to a radar device and a target height calculation method.
2. Description of the Related Art
Conventionally, an in-vehicle radar is designed mainly on the premise that systems, such as ACC (Adaptive Cruise Control) or PCS (Pre-Collision System) are used. A detection target of the system is a target at risk of a collision. However, since an in-vehicle radar which is currently available does not have a function of calculating a vertical azimuth, the height of the target from the ground surface cannot be grasped. In such a radar, as illustrated in FIGS. 22A and 22B, when a signboard, a fallen object, or the like on a roadway is detected, the detected object is erroneously recognized as a front target, so that the ACC and PCS may accidentally operate.
For this reason, as a method of recognizing a front target without falsely detecting the signboard or fallen object on the roadway as a running vehicle on a roadway, method of squeezing a vertical beam or a method of detecting change in electric power by multipass detection can be considered.
However, in the method of squeezing a vertical beam and the method of detecting change in electric power by multipass detection, there was a problem that it was difficult to appropriately recognize only a front target without falsely detecting a signboard or a fallen object on a roadway as an inappropriate target as described above.
Specifically, as for the method of squeezing a vertical beam, since a highly reflective target such as a big signboard is detected and thus it is falsely recognized as a front target even a vertical beam is squeezed, this method cannot appropriately recognize only a front target. In the method of squeezing a vertical beam at an inclined place such as a slop way, since there is a case where it becomes impossible to detect a front target, a front target cannot be appropriately recognized.
On the other hand, in the method of detecting change in electric power by multipass detection, since it is difficult to fully grasp the behavior of change in electric power by the multipass detection even based on the assumption of specular reflection when a target within a short distance is accidently detected, it is difficult to appropriately determine whether the target is a signboard or a fallen object on a roadway, or not. In the method of detecting change in electric power by the multipass detection, a false decision may be made in case of a target having a complicated shape because a true reflection point is unknown, so that a front target cannot be appropriately recognized.